This invention relates to safety covers for the needle of a hypodermic syringe and, more particularly, in a hypodermic syringe having a barrel with a needle extending outward therefrom, to a retractable safety cap for covering the needle to prevent accidental needle-stick therefrom comprising a unitary cap assembly of a resiliently flexible plastic material including a hub portion disposed concentrically about a base portion of the needle and attached to the barrel, a sliding safety hub portion having a bore therethrough slidably disposed with the needle passing through the bore and extending over a point end of the needle, and a plurality of slats extending between the hub portion and the sliding safety hub portion, the slats being spaced from one another along adjacent edges thereof at radially equal intervals about the periphery of the needle and being parallel to the needle whereby a longitudinal compressive force against the sliding safety hub portion is resisted by a longitudinal compressive resistance of the slats which must be overcome before the slats will deform and flex outward from the needle to allow the sliding safety hub portion to slide along and expose the needle for use.
So-called "needle-stick" is a major problem among health workers such as doctors, nurses, and the like. Needle-stick is the accidental puncturing of the skin of a health worker while working with hypodermic syringes. Needle-stick, per se, is not a new phenomenon for health care workers. In the past, however, it was more of an inconvenience than anything else. The present level of activity of serum-transmitted diseases such as hepatitis and AIDS, however, has transformed needle-stick from a mere inconvenience to a major consideration for health care workers. When a health care worker is stuck, he or she must be tested for exposure to the various serum-transmitted diseases such as hepatitis and AIDS. Even if such diseases were never actually contracted from the invasion of the needle through the skin, the costs of such testing would be (and are) considerable. Unfortunately, the diseases are contracted by such accidental needle-stick. Thus, the health care worker who is stuck must suffer the mental anguish of possibly having contracted hepatitis or AIDS by virtue of the accident.
The typical syringe in use today is as depicted in FIG. 1 where it is generally indicated as 10. The syringe 10 has a cylindrical barrel 12 into which a cylindrical plunger 14 is slidable inserted at one end. A needle 16 is attached to the opposite end of the barrel 12. For ease of puncturing the skin of a patient, the end of the needle 16 terminates in an extremely sharp chisel point 18. The needle 16 is covered with a removeable cylindrical cap 20 which typically lockingly attaches to the barrel 12. To remove the needle cap 20 for use of the syringe 10, the cap 20 is rotated to unlock it from the barrel 12 and then removed from over the needle 16. Once the protective cap 20 is removed, the point 18 is exposed and available for unintended needle-stick. For example, the syringe 10 could be dropped and stick into the user or anyone in the area at any point of the body in the path of descent. The cap 20 is also replaced on the syringe 10 after use for safety purposes. That process itself is a major contributor to needle-stick as it is easy for the user to miss the opening to the cap 20 with the needle 16 and stick a finger which is holding the cap 20.
Needle-stick is not a problem which has gone un-noticed in the art. Unfortunately, with one exception which will be addressed shortly, those persons inventing with an eye to preventing needle-stick have not done so in a realistic manner. Typically, what is offered as a solution is a complicated hypodermic syringe construction which (while it may work to prevent needle-stick) is so complex as to drive the cost of a syringe beyond that which the health care industry is willing to pay. For example, one popular prior art approach is to have the needle 16 be mounted for automatic retraction into the barrel 12 after use. As can be appreciated, not only is such construction complex and, therefore, extremely expensive; but, it does not take into consideration how such parts can be produced. As can be appreciated, the cylindrical barrel 12 and plunger 14 of the prior art syringe 10 of FIG. 1 are easily and inexpensively produced employing injection molding techniques with plastic. The syringes come pre-sterilized in a plastic wrap and are discarded after a single use thereby minimizing the costs associated with each single injection.
The single known exception to the general and complete impracticality of prior art approaches to preventing needle-stick is that suggested by Dr. Marcial Alvarez in his 1979 U.S. Pat. No. 4,139,009. This is not to say that Dr. Alvarez's retractable needle cap is a complete solution to the problem. There are, in fact, problems with Dr. Alvarez's approach which account for the fact that despite the extreme nature of the problem and the fact that Dr. Alvarez's design has been available to the art for over eleven years, the Alvarez solution has not been adopted by the suppliers of syringes. What the Alvarez cap suggests, however, is that there can be a simple and inexpensive approach to solving the needle-stick problem employing standard disposable syringes. The Alvarez approach is depicted in greatly simplified form in FIGS. 2 and 3 wherein his retractable cap is generally indicated as 22. The cap 22 comprises a cylindrical hub 24 which attaches to the barrel 12 of the syringe 10 in the same manner as the prior art cap 20. An annular slider member 26 fits over the needle 16 adjacent the point 18. A plurality (four being suggested) of bowed members 28 (four being suggested) extend from the hub 24 to the slider member 26 and extend out over the point 18 of the needle 16 so as to completely encase the needle 16. In use, the slider member 26 can be pressed against the rubber cover of a bottle (to fill the syringe 10) or against the skin of a patient (to inject from the syringe 10). By pushing the syringe forward, the slider member 26 is urged backward along the needle 16 as the bowed members 28 bow outward to a retracted position as in FIG. 3. Alternately, the slider member 26 can be gripped and retracted as, for example, when doing an intravenous injection in which the positioning of the needle 16 must be observed.
On paper and as a first impression, the Alvarez apparatus appears to be an ideal solution to the needle-stick problem. When one contemplates the totality of its operation and investigates the practicalities of producing it on a commercial level, however, certain shortcoming become apparent. For one thing, it is virtually impossible to mold the retractable cap 22 of Alvarez. Moreover, if one counts the parts in the retractable cap 22 of Alvarez as depicted in the patent drawings, there are five parts to each cap. As those skilled in the art are readily aware, each part of a device adds to the cost of manufacture and assembly. When manually retracting the cap 22 of Alvarez by gripping the slider member 26, it can be seen and appreciated that it would be an easy matter to have a finger in the line of movement of the needle point 18 and be stuck by it. Moreover, with the cap 22 in its "safety" position of FIG. 2, if one were to longitudinally bump the slider member 26, it is highly likely that the slider member 26 would retract sufficiently to allow the point 18 of the needle 16 to stick someone sufficiently to puncture the skin. This can be seen with reference to the graph of FIG. 4. As soon as some longitudinal force is applied to the slider member 26 of the Alvarez cap 22, the slider member 26 begins to move back and expose the point 18 of the needle 16. What would be desirable would be a retractable cap which would perform as depicted in FIG. 5; that is, have a step force which must be overcome before the cap begins to retract. The step force should be sufficient to prevent retraction from normal bumping force. Even more ideal would be a way of locking the cap from retraction until actual retraction was desired.
Two approaches somewhat similar to Alvarez are contained in the 1988 patents to Hagen (U.S. Pat. No. 4,735,618) and Dombrowski et al. (U.S. Pat. No. 4,790,828).
Wherefore, it is an object of the present invention to provide a retractable safety cap for covering the needle of a hypodermic syringe to minimize the opportunity of needle-stick which is simple and inexpensive to manufacture.
It is another object of the present invention to provide a retractable safety cap for covering the needle of a hypodermic syringe to minimize the opportunity of needle-stick which is reliable in operation.
It is yet another object of the present invention to provide a retractable safety cap for covering the needle of a hypodermic syringe to minimize the opportunity of needle-stick which can be employed with prior art syringes without any necessity of modifying the syringe.
It is still another object of the present invention to provide a retractable safety cap for covering the needle of a hypodermic syringe to minimize the opportunity of needle-stick which has a safety threshold of force necessary to retract the cap which will avoid retraction from normal longitudinal bumping forces.
It is a still further object of the present invention to provide a retractable safety cap for covering the needle of a hypodermic syringe to minimize the opportunity of needle-stick which has a safety lock associated therewith which will avoid retraction until desired.
Other objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.